About a year ago I went through the same exact questions as you. I was looking at getting a
L3400, wasn't even considering a Grand L. I went to the dealer to try out the
L3400, and they had a
L3130 sitting right next to it. I looked at them side by side, and immediately noticed the size difference (the Grand Ls are wider, as well as weighing more). Also, since the
L3400 is an "economy" tractor, it was pretty bare bones. I wasn't looking for many bells and whistles, but the things that I did want (QA on the loader, a fully synchronized transmission, live independant PTO), I either couldn't get or had to pay to upgrade. Since all these features were standard on the Grand Ls, it really shifted my thinking. Factoring in these items and driving the GST (vs. the straight gear shift of the 3400), the 3130 became a no-brainer for me.
Also, you said you were thinking about a backhoe in the future. If you go with the Grand L 3130 with an LA723 loader (which is the largest loader you can get with the
L3130), you can get the BH90 backhoe from Kubota. Someone correct me if I'm wrong on this, but I'm pretty sure you can only get the BH75 backhoe with the
L3400.
If you're really worried about the HP difference, then look at the
L3430 (if it's in the budget), but I've yet to run into an HP problem with the
L3130. I plow a 1/4 mile driveway for me and my neighbor using my 7' rear blade (gravel in the summer, snow in the winter), and it'll pull a full load of gravel uphill in low gear with no problem. If I get too big of bite into something, I always loose traction way before the engine would bog down. Granted, I do things in low gear (1-4 on GST, I'm never in a rush when using the tractor), but its got a ton of torque and power for anything I'd ever do with it.
I've just started bush hogging this spring, but so far it runs a 5' KK rotary cutter like it isn't there. I've read a lot of posts of 3130 owners running a 6' cutter without any problems, depending on how "rough" your cutting is.
Overall, I think you'll get more than your money's worth going to the
L3130. It has enough important upgrades to make it well worth the money, IMHO. Good luck with your decision.